Polyorganosiloxane block copolymers have already partly been described in the literature. For example, in the procedures disclosed in U.S. Pat. Nos. 3,678,125 and 3,678,126 and German Patents 2,142,594, 2,142,595 and 2,142,664, an organic monomer is polymerized with mono- or polyfunctional lithiumorganic initiators and hexamethylcyclotrisiloxane is subsequently polymerized to the resulting lithium functional polymers. In this manner, molecularly uniform block copolymers of configurations AB, BAB or AB.sub.n are obtained and, through subsequent coupling reactions, also those of configurations ABA, (AB).sub.x or (BAB).sub.x.
However, no block copolymers can be obtained by this procedure, which are branched in the polyorganosiloxane chain, i.e. which belong to the configuration type BA.sub.n, wherein B is a single or multiple branched polyorganosiloxane block and A is a linear organic polymer block, or whose polyorganosiloxane blocks still contain one or more silicon-functional groups, such as, for example, silicon-hydrogen or silicon-halogen groups.
Moreover, only hexaorganocyclotrisiloxanes can be used as starting compounds for the synthesis of the polyorganosiloxane blocks according to this prior art anionic polymerization procedure. Hexaorganocyclotrisiloxanes, however, belong to the less accessible, more expensive substances among the low-molecular weight, organosilicon compounds.
It is furthermore known from U.S. Pat. No. 3,244,664 that mono- or polyalkalifunctional organic polymers react with acyclic organosiloxane compounds containing 2 to 12 silicon atoms and at least two halogen, alkoxy, amino or alkylthio groups bound to silicon. This reaction yields terminally silyl-modified, organic polymers. This procedure thus results in polymeric materials in which organic polymer blocks are linked together by short organosiloxane blocks. The organosiloxane blocks of these compounds are, however, not equilibrated prior to their reaction with the polyalkalifunctional polymers, i.e., their average molecular weights are not in approximate statistical equilibrium. Consequently, materials are obtained by this synthesis, whose properties are not clearly reproducible. As a result of their short, non-equilibrated organosiloxane blocks, these systems furthermore possess only incompletely those properties which are characteristic of block copolymers as, for example, two glass transition temperatures, micelle formation, phase separation as well as compatibility with the two corresponding homopolymers and emulsifier activity.
German Pat. No. 1,720,855 furthermore discloses the reaction of at least partially equilibrated polyorganosiloxanes of the general formula EQU R'.sub.x SiO.sub.y (SO.sub.4).sub.z X.sub.4-(x+2y+2z)
wherein
R' is a monovalent hydrocarbon group, PA1 X is halogen atom which can partly be replaced by the --OSO.sub.3 H group and PA1 x = 1.5 - 2.1, PA1 y = 0.5 - 1.3, PA1 z = 0.0001 - 0.2 and PA1 4 = &gt;(x+2y+2z)&gt;2, PA1 R is alkyl or aryl, PA1 in the average molecule, a = 2 - 200 and b = 0 to 50 PA1 the ratio of R groups which are bound to Si atoms that are not trifunctional, to such R groups which are bound to trifunctional Si atoms being at least 4, PA1 are reacted with terminally organoalkali-functional, organic polymers, under splitting off alkali halide or alkali sulfonate. PA1 X represents chlorine and/or the R'SO.sub.3 group, R' being methyl or p-tolyl, PA1 R is methyl, PA1 a = 6 to 100 and PA1 b = 0 to 10. PA1 (a) Mixtures of organohalogen silanes such as, for example, (CH.sub.3).sub.2 SiCl.sub.2 or CH.sub.3 SiCl.sub.3 and polyorganosiloxanes, especially cyclic polyorganosiloxanes such as, for example, [(CH.sub.3).sub.2 SiO].sub.4.
with terminally alkalifunctional hydrocarbon polymers, to form block copolymers, the corresponding alkali salts being split off.
Block copolymers, which contain these polyorganosiloxanes as constituents, do, however, exhibit some disadvantages both in their method of preparation and in their properties. The equilibration of polyorganosiloxanes with H.sub.2 SO.sub.4 proceeds gradually slower with increasing molecular weight of the polyorganosiloxanes, since the catalyst is consumed by being incorporated in the polyorganosiloxane chain. In addition, the viscosity of the resulting products becomes uncomfortably high. Furthermore, the stability of the block copolymers made with these polyorganosiloxanes, particularly at elevated temperatures and in the presence of moisture, is inadequate and the compounds tend to discolor at elevated temperatures. This deficient stability and the tendency to discolor are caused by the presence in the block copolymer of residual H.sub.2 SO.sub.4, which was used to equilibrate the starting siloxanes.